NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Parallax of the Moon
From: Stan K
Date: 2015 Feb 7, 05:03 -0500
From: Stan K
Date: 2015 Feb 7, 05:03 -0500
Please ignore all messages from me with the subject "Parallax of the Moon". To start with, I did not give all the information required in the original question. Then.more mistakes. I should not be doing this when I should be sleeping. Now I almost have my head removed from my butt, but not quite.
Stan
-----Original Message-----
From: slk1000 <slk1000@aol.com>
To: slk1000 <slk1000@aol.com>; navlist <navlist@fer3.com>
Cc: ronandsandy <ronandsandy@olympus.net>
Sent: Sat, Feb 7, 2015 4:44 am
Subject: Re: Parallax of the Moon
From: slk1000 <slk1000@aol.com>
To: slk1000 <slk1000@aol.com>; navlist <navlist@fer3.com>
Cc: ronandsandy <ronandsandy@olympus.net>
Sent: Sat, Feb 7, 2015 4:44 am
Subject: Re: Parallax of the Moon
Uh oh... Now I'm not so sure.
-----Original Message-----
From: slk1000 <slk1000@aol.com>
To: navlist <navlist@fer3.com>
Cc: ronandsandy <ronandsandy@olympus.net>; slk1000 <slk1000@aol.com>
Sent: Sat, Feb 7, 2015 2:47 am
Subject: Re: Parallax of the Moon
From: slk1000 <slk1000@aol.com>
To: navlist <navlist@fer3.com>
Cc: ronandsandy <ronandsandy@olympus.net>; slk1000 <slk1000@aol.com>
Sent: Sat, Feb 7, 2015 2:47 am
Subject: Re: Parallax of the Moon
I asked this question a couple of days ago and I cannot believe I have not received one response. Dozens of responses on "Irregular Quadrilateral Center" and "Japanese Sextant 1979", but none on this question. Well, last night I was sitting on the couch watching Hawaii Five-0 when I had an epiphany. I was using the formula on page 280 of the Nautical Almanac, PA = HPcosH+OB, where HP is the horizontal parallax, H is the apparent altitude (sextant altitude corrected for index error and dip, H = Hs + I - D), and OB is the correction for the oblateness of the Earth. It might be said that the first part of the formula, HPcosH, is just an approximation, but it is a very good approximation. The problem is much more basic than that. THE FORMULA IS INCORRECT! Now I will play Frank Reed and challenge you to tell me why. It is really pretty simple once you give it a little thought.
Stan
-----Original Message-----
From: slk1000 < slk1000@aol.com>
To: navlist < navlist@fer3.com>
Cc: slk1000 < slk1000@aol.com>
Sent: Thu, Feb 5, 2015 6:07 pm
Subject: Parallax of the Moon
From: slk1000 < slk1000@aol.com>
To: navlist < navlist@fer3.com>
Cc: slk1000 < slk1000@aol.com>
Sent: Thu, Feb 5, 2015 6:07 pm
Subject: Parallax of the Moon
The attachment is part of an output from the USNO Celestial Navigation Data web page. Can anyone tell me how the USNO gets a parallax value of 15.6'? Every other source I tried got about 15.27', but 15.6' is the only one that makes the numbers agree with the Moon Altitude Correction Tables in the Nautical Almanac.
Stan
